Flood watches issued for B.C.'s South Coast and Lower Fraser regions as atmospheric river arrives

UPDATE — Dec. 5, 2023: Heavy rain, wind pummel southwestern B.C. as atmospheric river makes landfall

Torrential rain, heavy snow, strong winds and high tides converged on coastal and southern British Columbia Monday.

The province's River Forecast Centre issued flood watches for rivers and streams in Metro Vancouver, the South Coast and the Lower Fraser regions, while Vancouver Island and the Nicola and Similkameen regions are under high streamflow advisories.

Environment Canada said Monday a "potent and impactful" atmospheric river was set to make landfall on southwestern B.C., with as much as 150 millimetres of rain predicted for Western Vancouver Island.

A flood watch is the second level on the provincial forecast centre's three-tiered warning system. It means that river levels are rising, and flooding in areas adjacent to riverbanks may occur.

"Current forecasting is suggesting that flows are expected to be highest for West Vancouver Island, the North Shore Mountains, and the Lower Fraser Valley, however this could shift into nearby areas if higher than forecasted rainfall occurs in other areas," reads the flood watch.

The forecast prompted the Transportation Ministry to order a 20-kilometre stretch of Highway 1 south of Lytton closed starting Monday night until Tuesday morning because of the danger of heavy rain undermining stability of the area.

"The ministry's geotechnical experts have recommended this closure as a precaution in case heavy precipitation overwhelms the area affected by this summer's Kookipi Creek wildfire," the ministry statement said.

"Checkpoints will be set up on Highway 1 just outside of Hope and Lytton to advise motorists about the detour routes and assist local traffic."

The ministry said drivers can use highways 3 or 5 as a detour, but it warns that the storm is also bringing rain, snow and winter driving conditions to those routes.

Inland Vancouver Island, the Howe Sound region and parts of Metro Vancouver, including the North Shore, Coquitlam and Maple Ridge, were expecting up to 100 millimetres of rain.

In Greater Victoria and Metro Vancouver, Environment Canada was also forecasting high tides exceeding normal levels that may cause minor coastal flooding to exposed shorelines, an advisory that has since been lifted.

Further north, winds gusting up to 120 km/h prompted warnings from the weather agency on Monday for northern Vancouver Island, Prince Rupert and Haida Gwaii.

B.C. Hydro reported that a downed tree across power lines caused an outage affecting about 1,400 customers on Graham Island in Haida Gwaii for much on Monday.

The atmospheric river was also expected to hit the southern Kootenay region in B.C.'s Interior, with the Elk Valley near Fernie and parts of Highway 3 expecting up to 100 millimetres of rain starting late Monday and lasting until Thursday.

Environment Canada said drivers on the Sea to Sky Highway from Squamish to Whistler and the Coquihalla Highway from Hope to Merritt should be cautious of heavy rains that could raise the risk of flooding and landslides along the routes.

The agency also issued a winter storm warning for the Trans-Canada Highway from Sicamous to Golden, with up to 15 centimetres of snow expected, along with ice pellets and the possibility of freezing rain.

An atmospheric river is a term used to describe large streams of water vapour that can bring heavy amounts of rain and precipitation, particularly in mountainous areas like the South Coast.

A little over two years ago, an atmospheric river brought devastation to much of southern B.C., causing widespread flooding and washed out highways.

The province says it has already deployed sandbags to 27 First Nations and local governments as the storm pounds southern B.C.